The effect of two training procedures on the development of reading speed in poor readers is examined. One training concentrates on the words the children read correctly ("successes"), the other on the words they read incorrectly ("failures"). Children were either informed or not informed about the training focus. A randomized controlled trial was conducted with 79 poor readers. They repeatedly read regularly spelled Dutch consonant-vowel-consonant words, some children their successes, others their failures. The training used a computerized flashcards format. The exposure duration of the words was varied to maintain an accuracy rate at a constant level. Reading speed improved and transferred to untrained, orthographically more complex words. These transfer effects were characterized by an Aptitude-Treatment Interaction. Poor readers with a low initial reading level improved most in the training focused on successes. For poor readers with a high initial reading level, however, it appeared to be more profitable to practice with their failures. Informing students about the focus of the training positively affected training: The exposure duration needed for children informed about the focus of the training decreased more than for children who were not informed. This study suggests that neither of the two interventions is superior to the other in general. Rather, the improvement of general reading speed in a transparent orthography is closely related to both the children's initial reading level and the type of words they practice with: common and familiar words when training their successes and uncommon and less familiar words with training their failures. (Contains 4 figures, 4 footnotes, and 6 tables.)